<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>jquery</title>
    <script src="./js/jquery-3.4.1.min.js"></script>

    <script>
        $(function () {
            // alert("HelloWorld!")
            $("div span").css("font-size","50px");
            jQuery("div span").css({"background":"#ff0000","color":"#ffffff"})

        });

    </script>

</head>
<body>
<div>
    <span>Hello</span>
</div>
<div>
    <span>World</span>
</div>
<span>!!!</span>

</body>
</html>